Equine coronary artery responds to 5-hydroxytryptamine with relaxation in vitro |
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Authors: | T OBIT A KABEYAMA A NISHIO |
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Institution: | Department of Veterinary Pharmacology, Faculty of Agriculture, Kagoshima University, Kagoshima 890, Japan;Department of Veterinary Pharmacology, Faculty of Agriculture, Kagoshima University, Korimoto 1–21-24, Kagoshima 890, japan |
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Abstract: | Isolated equine coronary arteries responded to 5-hydroxytryptamine (5-HT) with relaxations in both endothelium-dependent and endothelium-independent mechanisms. Experiments were designed to characterize the 5-HT receptor sub type mediating these relaxations. Both 5-HT and alpha-methyl-5-HT (α-Me-5- HT; 5-HT2 agonist) produced concentration-dependent relaxations in equine coronary arteries precontracted with a thromboxane A2 derivative (0N011113). The degree of the maximal relaxation induced by α t-Me-5-HT was about one-half of that induced by 5-HT. In the coronary arteries without endothelium, α -Me-5-HT produced no relaxation, but 5-HT caused relaxation, which was inhibited by a 5-HT1 antagonist (methysergide, mianserin and methiothepin), but was inhibited neither by ketanserin (5-HT2 antagonist) nor by MDL72222 (5-HT3 antagonist). In the coronary arteries with endothelium, however, the relaxation induced by α -Me-5-HT was inhibited by ketanserin, L-nitro-arginine (NO synthase inhibitor) and methylene blue (soluble guanylate cyclase inhibitor). These results suggest that the relaxation induced by 5-HT in equine coronary arteries depends mainly on the stimulation of both 5-HTi receptor subtype on smooth muscle cells directly, and 5-HT2 receptor subtype on endothelial cells indirectly by liberating endothe-lium-derived NO. |
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